Wood preservation composition and method



lee-18.29 @R i xx 0222A XR 3,061,506 A f 1 Oct. 30, 1962 R. M. MORRISS,JR.. ETAL 3,

- woon PRESERVATION composmon AND METHOD Filed March 51, 1960 O/LABSORPTION CHARACTERISTICS was PERFORMANCE IN REDUCING EXUDATION 2 E \@Ey 60 Q i w v Q 5 It) 1K v c b 40 E MU L @N S 0@ d 30 E m 59 5 l0 I5 20PEREZ-INT max 10 FORM GEL L REUBEN M. Mom/s5, JR.

' BY hufldy.

RALPH G $144M ALLEN ATTORNEY United States Patent Dfi 3,061,508 e WOODPRESERVATION COMPOSITION AND METHOD Reuben Mooras Morriss, Jr.,. St.Louis, and Ralph G.

Van Allen, Crestwood, Mo., assignors to Wood Treating Chemicals Company,St. Louis, Mo., .a corporation of Missouri Filed Mar. '31, 1960, Ser.No. 19,090

' 14 Claims. (Cl. 167-42) The'present invention relates'to.thepreservation of wood and protecting it from attack by various organismsincluding insects, plant and marine organisms. More particularly, thisinvention provides a mixture readily incorporated into wood byconventional commercial'treating practices which will impart the desiredwood preservative 3,061,508 Patented Qct. 30, 1952 ice 183 to 191, andUnited States Patents 1,556,570; 1,609,- 642;'1,648,294; and 1,648,295.

In these processes, increased costs are involved due to the necessity ofkeeping the treating solution at relatively high temperatures at alltimes, thus requiring steam jacketed or otherwise heated storage tanks,pipe lines and the like. Furthermore, large volumes of blocking agentsare required with resultant increased costs of materials'as well asappreciable increased weight of the treated wood items even after someof the carrier has been removed.

It is an object of the present invention to provide a wood treatingcomposition that will be retained within the wood after application witha'minimum of loss by bleeding.

Itis a further object of the invention to provide a 7 liquid woodtreating composition that can' be applied f without expensive heatingequipment necessary formainforcingof various compositions into wood toimpart preservative value to the treated wood. This protection aimedeither to poison the wood so that fungi or insects would not consume thewood, or to add materials that would fill the cell voids with a waterexcluding or water repelling material, thus reducing the moisture heldby the fibers. to a point below the moisture requirements for fungusgrowth. In the former category would fall such products as the oilpreservatives (creosote, creosote coaltar, etc.), the oil-bornepreservatives (pentachlorophenol,

copper naphthnate, etc.) and the water-borne preservaa treatment. Insome cases this bleeding maytake place soon after treatment; in othercases it may occur some time later when the treated wood is in storageyards or when the wood is placed in service.

Such losses are undesirable not only because of the problems involved inhandling the wood which is wet with exudate, but also because of theloss of preservative which means that it is no longer in the wood toexert its preservative effect.

Attempts have been made by various methods toprevent this bleeding. Qnepractice known to thewood preservation industry is to steam the woodafter treatment, thus heating and expanding the treating solution in theouter cells of the wood so that it bleeds while the wood is still in thetreating vessel. Such bleeding removes some of the treating solutionfrom the outer wood cells and if solution from deeper in the wood latermoves outward, it enters the unfilled surface and near-surface cellsrather than oozing (bleeding) out of the wood. a I

Another methodthat has been employed "is to use blocking agents whichare in solution when applied to the wood, but-which solidify later toblock the movement of liquid preservative solution from the surfacecells. Also, wood has been impregnated with high melting point waxes toproduce water repellency. Coollidge disclosed the use of montan wax forsuch purposes in the 1926 Proceedings of the American Wood-PreserversAssociation, pages taining normally-solid materials in a liquid state.

It is a further object of the invention to provide a wood treatingcomposition that can be' applied at reduced cos and will beretained-within the wood with loss by bleeding. I A further object ofthe invention is 'to' provide a process for treating wood that isefficient and economical and will provide extended life'of the treatedwood.

- It is a further object of the invention to provide a wood treatingcomposition that holds a toxicant in its distributed positionswithinthe' wood because of reduced movement of the-whole woodpreservative composition within the wood. s

A further object of the invention-is to provide a wood treatingcomposition wherein the concentration of toxicant in agiven treated areawithin the wood is increased because the solvent leaves the wood byvolatilization rather than by movement of the whole solution.

A further object of the invention is to provide a wood treatingcomposition including a wax which holds a toxicant distributed deeply'within the treated wood.'

The present inventionresides in the concept of a wood treating mixtureincluding a preservative and wax or mix tureof waxes which, when used asa treating solution, have the capacity to form a crystalline latticewith intercellular crystal spaces or apertures between crystalsthereofthat will permit-a large quantity of the preservative to be held to thewax crystals and within-the inter-crystalline spaces. Thereby, themixture forms a" gel after impregnation into the wood, said gel servingto fix the preservative substantially within the wood and reduce.

exudation of the preservative from the wood. -The preservative used canbe a single chemical toxicant or a mixture of toxicants with or withouta carrier depending upon the nature of the preservative.

, The mixture or composition of the invention provides for woodpreservation at various temperatures and pressures. At relatively lowtemperatures, when the wax is solid, the, above-described latticefixes-the carrier and toxicant within the wood and prevents exudation.At higher temperatures. such as those achieved when. treated poles areexposed to sunlight, the waxes employed according to the inventionreduce exudation and loss of the toxicant because of their molecularsize andconfigura- I tion which influence viscosity. ;At theseelevatedtemin h h whole original solution.

3 point and crystallization point occur is' significantly raised. In thestatic system there also seems to be a retentive capacity of the waitmolecule for the oil even though the lattice has not formed throughcrystallization of wax from solution. This issubstantiated by theresults obtained by various waxes in reducing exudation of preservativefrom wood'(column 14 in table). As described below, the tests reportedin the table were conducted and'the test blocks maintained at atemperature (180 F.) well above the solution temperature of the It isalso noted that the cloud point of the preferred combination exists overa broad range of temperatures and this contributes to blocking of thepit membranes and other apertures which prevent oil movement through thewood structure.

At temperatures where essentially the solid state exists, the waxemployed in the mixture of the invention acts similar to a sponge tohold the carrier oil and toxicant within its crystalline lattice. Bythus holding the car? rier and toxicant in the lattice, the motility ofthe carrier and toxicant is reduced and the overall mixture assumes thenature of a gel. The wax musthave a desired spacing between crystalsthereof. If the crystals are too small, as in certain microcrystallinewaxes, there is insufficient room between the crystals to accommodateand hold sufficient quantities of the carrier and toxicant to give thedesired effect. On the other hand, if the wax crystals are too large,there is less surface area of crystal per unit volume for adsorbing thecarrier oil, and the holding power of the wax for oils is insufiicient.

' Molecular configuration is another important factor in selecting asuitable wax for the mixture of the invention. Straight chain or normalparaflin waxes are undesirable per se because they form large crystalswith excessively large openings therebetween. The surface tension of thecarrier oilv may be and generally is insutficient to hold the carrieroil andtoxicant in these relatively large inter-crystalline spacings.The selection of the wax thus depends upon more than one characteristicof the wax. Among the important characteristics are the molecularweight, the configuration of the molecule and the crystalline latticesize in which it can be crystallized. It will be apparent from the abovediscussion that the sizev of the spacings between the crystals is;important. It has been shown that there is an optimum range of spacingsize between upper and lower ranges which is suitable for reducing theloss of the oil carrier and toxicant from treated wood. The numericalsize of the desirable spacings between crystals is not yet known nor isa method known of making such measurement. However, according to theinvention, numerous suitable waxes have been found which produce thedesired results. Certain properties of these waxes have been measuredand desirable ranges established so as to define the limits of theinvention.

Among the physical properties of the waxes suitable for the compositionand method of the invention are the following with the desired ranges:

While certain microcrystalline waxes fall within the range of thisinvention, a preferred wax would be defined as a distillate intermediateparaflin wax. A wax so described and falling within the preferred rangeof phys ical characteristics as indicated above would be one which, whencombined with the toxicant and petroleum carrier, would penetrate thewood structure and not be filtered from solution to any great extentunder the conditions of commercial application. Waxes of highermolecular weight (e.g. microcrystalline waxes) will in general befiltered from solution, thus changing the distribution characteristicsof the preservative solution.

A desirable wax for the mixture of the invention would be one whichwould produce a very viscous solution throughout a normal range oftemperatures roughly up to F.; but which when heated to temperaturesused in wood treating applications, would thin out sufliciently topermit penetration of the wood.

The molecular size and configuration of the wax are also importantfactors in selecting a wax for the invention. Such a wax should have asubstantial quantity of non-nonnal or branch-chained paraffins such asiso-parafiins, mcnocycloalkanes as well as other cyclic hydrocarbons.

Seven examples of w which can be used as illustrative but which are 11be construed as limiting the scope of this patent, and which haveimparted the desired characteristics to a preservative are petroleumhydrocarbon waxes of the microcrystalline residual and intermediateparafiin distillate waxes designated C, D, E, F, H, I, and K in thetable below.

While pure or substantially pure waxes can be employed, less-refined orcrude waxes can also be used which contain various amounts of residualoils. Further, blends of waxes can be employed to provide wax mixtureshaving properties as set forth above. For example, parafiin waxgenerally has a crystal structure with large crystais and largeinter-crystal spaces. On the other hand, microcrystalline petroleum waxhas a crystal structure with small crystals and small inter-crystalspaces. By blending relatively small quantities of certainmicrocrystalline petroleum wax with relatively large quantities ofcertain normal parafiin wax, a. blend can be obtained having crystalstructure suitable for use in the wood treating composition of. theinvention.

The ax is desirably employed in amounts generally not greater than 10%by weight of the entire mixture. Particularly advantageous results areobtained using 1% to 2% by weight of the preferred wax types.

Among the to icmts which can be employed are: oilborne preservativessuch as pentachlorophenol and copper naphthenate; oil preservatives c ascreosote, creosote coal-tar and the like; et cetera.

Among the carrier or solvents which can be employed are petroleum oilsolvents such as heavy and light solvent petroleums designated as AWPAP9 oils (American Wood-Preservers Association), and equivalent oilsolvents or carriers.

The treatment method according to the invention includes applying themixture to wood by impregnating the wood with the mixture. Conventionalpressure, thermal and vacuum processes can be employed. The following isa specific example of the mixture and method according to the invention.

Mix in a kettle the following three ingredients:

8.9 pounds of distillate intermediate paraffin wax melting at 159.6 F.as determined by American Society of Testing Materials, bulletin D-87,having a refractive index n of 1.4305, a viscosity measured at 210' Ref51.4 Saybolt Universal seconds and designated as wax E in the tablebelow.

Agitate the mixture for approximately 30 to 45 minutes while maintainingthe temperature at about 160 F. until a clear solution is obtained.

-As an example of employing the mixture in treating one specie of wood,place two Douglas fir 7-foot post in green condition, in an experimentalpressure treating cylinder. Heat the contents of the cylinder to about185 F., simultaneously drawing a vacuum until the pressure within thecylinder is about 15 to 25 inches of mercury. Maintain these conditionsfor about an 11 hour period to remove approximately 7 pounds of waterper cubic foot of wood. Next, remove the solution irom the cylinder andstore in a separate tank- Apply 25 pounds per square inch air pressureto the interior of the cylinder. Fill the cylinder with the preservativesolution while maintaining the internal pressure of 25 pounds per squareinch. Next, apply pressure by means of a pump to raise the pressurewithin the cylinder to about 120 pounds per square inch and maintainthis pressure for a period of about 3 hours at an average temperature of160 F. This pressure forces the preservative solution into the posts.

It was desired to obtain a net retention of 8.0 pounds of preservativesolution per cubic foot of wood. In order to accomplish this, injectapproximately 10.0 pounds of preservative solution per cubic foot ofwood. Next reduce the pressure within the cylinder to atmosphericpressure. Drain the solution from the cylinder. Apply a vacuum of 22inches of mercury for a period of 45 minutes to strip excesspreservative solution from the wood surface. Thus two posts are producedwhich are impregnated with the preservative solution and wax additive,having a net retention of 9.7 pounds of the applied composition percubic foot of wood.

The following table gives data on numerous experiments employingdifferent preservative solution compositions used for treating woodspecimens. The data designated as the control were based on specimenstreated with a 5% "by weight solution of pentachlorophenol in an AWPA P9oil without any wamqfifi'g' sbmns were made from samples of the controlby adding 1% by specific ponderosa pine specimens, each set. ofspecimens being treated in only one of the solutions, according to thefollowing procedure:

Four specimens of ponderosa pine were immersed as indicated above ineach of the solutions, a vacuum applied to draw air outwardly from thewood specimens to permit the entry of the solutions. Next'the pressurewas raised to atmospheric pressure so that the increase in pressurewould force the solution into the wood specimens. Thereafter thesolution was drained from the treating vessel and a final vacuum appliedto strip excess solution from the surface of the wood. Matched blocks ofwood were employed and uniform pressures, tempcramres, treating timesand other conditions were employed in order that direct and reliablecomparisons could be made on each set of specimens between testsolutions or wax additives.

Each block (specimen) was weighed prior to treatment and after treatmentto determine the amount of preservative solution retained therein. Afterthe foregm ing treatment to impregnate the blocks with solution, eachblock was suspended over a tared beaker in a chamber having controlledconditions. Next, the chamber was heated to raise the temperature fromroom temperature to 160 F. over a two-hour period to produce exudationof the solution from the wood. The heating was con tinued to raise thetemperature from 160 F. to 180 P. so as to produce an averagetemperature in the center of the blocks of about 170 F. This three-hourheating cycle was repeated each day over a period of 20 days. At the endof this period, the tared vessel was weighed and the amount of exudatedetermined. In the case of compositions employing waxes A through 0 inthe table, column 14 was computed by subtracting the percent exudationfrom the treatment with each wax preservative solution from the percentexudation of the control. This difference was divided by the percentexudation of the control and multiplied by 100 to determine the percentreduction in exudation.

Wood treating compositions containing waxes C, D, E, F, H, I, and K inthe table are within the scope of the present invention. It will benoted from column 14 of the table that these waxes, when mixed to formpreservative solutions according to the invention, produce a dramaticreduction in exudation from the wood specimens. Thus the useful life ofthe wood under service conditions is extended. Furthermore, theappearance of the wood is improved because of controlled exudation.

Table War nee- Redue Ran-so Vis- Ponr essary Aver- Avertion in ASTM tlveooslty lnt to form age age Urea Normal 1so Mono- Dicyclm Mono; exuda-Wax Type 287) index (war) 1 a wax gel in nummolecreactoalkaues, alkanes,eycloalkanes, tion ,P, 100 SSU at solu. in AWPA her ular bis, perpercentpercent alkanes, percent percent irom F. a" 210 F, AWPA P9 oil at carbonweight cent percent wood,

P9011 75 F., atoms percent percent +7 3 124. 3 1. 4184 35. 3 12 24. 5 24338 95. 6 2. 3 1. 8 0. 3 5. 7 3 132. 8 1. 4212 39. 3 10 17. 7 20 366 88.4 4. 5 0. 0 0. 9 0. 2 25. 4 2 139.1 1. 4239 41.5 15 10.0 27 380 82.5 6.4 0.1 1.5 0. 4 38.4 2 140. 2 1. 4244 41. 1 +18 10. 0 28 395 81. 0 B. 59. 0 2.1 0. 5 34. B 2 159. 6 1. 4305 51. 4 +25 6. 0 34 478 67. 5 7. 517. 3 6. 2 1. 5 63. 8 1 175. 4 1.4413 77. 8 11. 5 -00 1 141. 3 1. 4435N. 0 +14 25. 4 20-35 0 1 181. 5 75.0 8. 56 50-00 1 181. 5 1. 4368 75. 0+15 8. 56 50-00 49. 7 1 166. 5 1. 4496 89. 8 15. 50 45-65 1 170. 0 1.4305 77. 0 +11 10.00 45-65 50. 5 1 160. 0 1. 4427 01. 1 +10 10. 5 M 39.2 4 $10.0 +10 10. 0 39. 5 5' 1M. 0 +10 12. 7 35. 0 5 186. 0 270.0 +1311.0 20. 3

t-resldual-mlcmcrystalltne, 2-dlsti1late intermediate peramn,a-dlsttilste-peramn, 4-synthetie-Flsher Tropsch-lso penifin, ti-vegetable,

d-mineral-lignite extract.

I No wuonly the mixture 0! pentachlorophenol and AWPA P0 oil.

weight of each of the waxes designated A through 0 in Each treatingsolution desigthe table to each sample.

nated A through 0 was used separately to treat four percent reduction inexudation, column 14 of the table,

is plotted as ordinate and percent wax required to produce a gel, columnof table, as abscissa. From the data plotted in this graph, it will beseen that the lower the percentage of wax required to produce a gel, thegreater the reduction in exudation. It would appear that this provides aprocedure for identifying waxes suitable for the invention. That is,where a low percentage of a wax is required to produce a gel, such a waxmerits further investigation to determine if it comes within the scopeof this patent disclosure.

Thus it will be seen that the invention provides a composition forpreserving wood having increased etficiency and a method of applyingsame to wood. The invention provides an increased useful life of woodtreated with the solution, which results in an economy of treatment.

While a present preferred embodiment of the invention has beendescribed, it will be understood that various modifications of theinvention can be produced within the scope of the appended claims.

We claim:

-I. A composition for preserving wood which comprises a resegyative forcombating biological attack on wood, an ax having an average molecularweight not exceeding 600, a viscosity between about 40 and 80 SayboltUniversal seconds at 210 F., said wax being crystallizable intocrystalline forms capablo of forming gels and holding the preservativewithin the crystalline structure.

2. A composition for preserving wood which comprises a toxicant forcombating biological attack on wood, a hydrocarbon carrier, and a waxhaving an average mole'cular weight between about 350 and 600 and aviscosity between about 40 to 80 Saybolt Universal seconds at 210' F.,said wax being crystallizable to form a crystalline lattice capable ofadsorbing said hydrocarbon carrier to form a gelled mixture.

3. The invention as set forth in claim 2 wherein said wax is present inabout 1% to 2% by weight of the entire mixture.

4. A method of preserving wood comprising the steps of mixing apreservative for combating biological attack on wood with a wax havingan average molecular weight of not exceeding about 600, and a viscositybetween about 40 and 80 Saybolt Universal seconds at 210 F., andimpregnating wood with said mixture.

5. The invention as set forth in claim 4 wherein said preservative is ofthe oil-borne type.

6. The invention as set forth in claim 4 wherein said preservative is ofthe oil-type preservative.

7. A process for preserving wood comprising the steps of mixing atoxicant, a petroleum hydrocarbon carrier, and not more than of a waxhaving an average molecular weight from about 350 to about 600 and aviscosity between about 40 and 80 Saybolt Universal.

seconds, and, impregnating wood with said mixture.

8. A composition for preserving wood which comprises a wood preservativeand wax means having a molecular configuration to reduce the motility ofthe preservative in the liquid state, said wax means having a crystallattice in the solid state to form a gel of the preservative and thusreduce the motility of the preservative.

9. A composition for preserving wood which comprises a wood preservativeand a wax having a molecular configuration to reduce the motility of thepreservative in the liquid state, said wax having a crystal lattice inthe solid state to form a gel of the preservative and thus reduce themotility of the preservative, said wax having a viscosity, determined at210 degrees Fahrenheit, between about 40 and about Saybolt Universalseconds.

10. A composition for preserving wood which comprises a preservative forcombating biological attack on wood; and a wax having an averagemolecular weight not exceeding 600, a viscosity, measured at 210 degreesFahrenheit, between about 40 and about 80 Saybolt Universal seconds, arefractice index ri between about 1.4230 and about 1.4415, said waxbeing crystallizable into crystalline forms capable of forming gels andholding the preservative within the crystalline structure, said Waxmelting between about and degrees Fahrenheit, said wax being present inan amount not greater than about 10 percent by weight of thecomposition. 11. A composition for preserving wood which comprisespentachlorophenol; a petroleum hydrocarbon carrier; and a wax having anaverage molecular weight between about 350 and about 600, a viscositybetweenv 'about 40 and about 80 Saybolt Universal seconds, measured at210 degrees Fahrenheit, said wax being crystallizable to form acrystalline lattice capable of adsorbing said petroleum hydrocarboncarrier to form a gelled mixture.

12. A composition for preserving wood which comprises a preservative forcombating biological attack on wood; and an intermediate paraflindistillate wax that melts at about 159.6 degrees Fahrenheit, has arefractive index n of about 1.4305, and has a viscosity, meas; ured atabout 210 degrees Fahrenheit, of about 51.4 Saybolt Universal seconds,said wax containing approximately 67 percent normal alkanes, 7.5 percentisoalkanes and about 17 percent monocycloalkanes.

13. In the process of preserving wood which includes the steps ofapplying a partial vacuum to wood; subsequently applying a woodpreserving composition to the wood under a positive pressure to forcethe composition into the wood; the improvement which comprises saidcomposition including a preservative and wax means having a molecularconfiguration to reduce the motility of the preservative in the liquidstate, said wax means having a crystal lattice in the solid state toform a gel of the preservative and thus reduce the motility of thepreservative.

14. In a process of preserving wood which includes the steps of applyinga partial vacuum to wood and subse quently impregnating a woodpreserving composition into the wood under a positive pressure forcingthe composition into the wood; the improvement wherein said woodpreserving composition comprises a preservative and a wax having amolecular configuration to reduce the motility of the preservative inthe liquid state, said wax having a crystal lattice in the solid stateto form a gel of the preservative and thus reduce the motility of thepreservative, said wax having a viscosity, determined at about 210degrees Fahrenheit, between about 40 and about 80 Saybolt Universalseconds, said wax being present in an amount sutficient to reduce saidmotility but not greater than about 10 percent by weight of thecomposition.

References Cited in the file of this patent UNITED STATES PATENTSCarswell: lndust. and Eng. Chem., November 1939, vol. 31. No. ILPP-1431-1435,

12. A COMPOSITION FOR PRESERVING WOOD WHICH COMPRISES A PRESERVATIVE FORCOMBATING BIOLOGICAL ATTACK ON WOOD; AND AN INTERMEDIATE PARAFFINDISTILLATE WAX THAT MELTS AT ABOUT 159.6 DEGREES FAHRENHEIT, HAS AREFRACTIVE INDEX ND100 OF ABOUT 1.4305, AND HAS A VISCOSITY, MEASURED ATABOUT 210 DEGREES FAHRENHEIT, OF ABOUT 51.4 SAYBOLT UNIVERSAL SECONDS,SAID WAX CONTAINING APPROXIMATELY 67 PERCENT NORMAL ALKANES, 7.5 PERCENTISOALKANES AND ABOUT 17 PERCENT MONOCYCLOALKANES.